This is an industry sponsored (DuPont Merck) multi-centered dose escalating study to evalute the safety, tolerability, pharmacokenetics (PK) and pharmacodynamics (PD) of DMP 777 in adults with cystic fibrosis. Objectives are to evaluate safety, efficacy, PK and PD or multiple oral doses, administered at different doses or regimens, and to determine the dose required to sustain high-level systemic neutrophil elastase inhibition. The study theorizes that the amount of lung destruction in cystic fibrosis will be reduced if neutrophil elastase is neutralized.